Sculpting Lag and Freezing
See answers to question 3516

Dyntopo is increasing the density of the mesh for you as you sculpt and it is very demanding on performance at that resolution. To see this:


In Properties panel -> Object -> Display, enable Wire and Draw All
Edges.
Repeat your test of resolution 50 at constant detail on a default cube with dyntopo enabled


If you need to sculpt at this level of detail, you will have to upgrade some hardware.

Tablet vs. mouse is not relevant.